Field of the Invention
The present invention relates to color transformation processing of shooting data.
Description of the Related Art
The Academy of Motion Picture Arts and Sciences (AMPAS) is working to standardization of color adjustment in video production.
FIG. 1 is a block diagram showing the color transformation architecture of the digital movie production workflow standard AMPAS-IIF proposed by the AMPAS. The color transformation architecture of AMPAS-IIF is basically defined as association between two common color spaces and input and output devices.
The two common color spaces are an input color space 1503 and an output color space 1505. The input color space 1503 is ACES (Academy Color Encoding Specification), and the output color space 1505 is OCES (Output Color Encoding Specification). Transformation from an input device color space to the ACES color space is performed by input device transform (IDT) 1502. Transformation from the ACES color space to the OCES color space is performed by a reference rendering transform (RRT) 1504. Transformation from the OCES color space to an output device color space is performed by output device transform (ODT) 1506.
With the IDT 1502, video data of an imaging apparatus 1501 serving as an input device (data in a device color space) is transformed to video data in the ACES 1503 (data in a common color space). The video data in the ACES 1503 undergoes editing processing such as color adjustment. After that, the video data having undergone the editing processing is transformed to video data in the OCES 1505 by the RRT 1504. The video data in the OCES 1505 (data in the common color space) is then transformed to video data of a display device 1507 serving as an output device (data in a device color space) by the ODT 1506.
The ACES 1503 is defined as a color space with reference to a scene, and has values obtained by linearly transforming CIE (Commission Internationale de l'Éclairage) tristimulus values X, Y, and Z obtained by measuring the scene itself by a colorimeter. Furthermore, the chromaticities of the three RGB primary colors to cover the entire spectrum locus are determined, and encoded in 16 bits (16-bit float).
AMPAS-IIF provides the video production workflow with a standard. There are provided a mechanism of transforming various moving image materials to the ACES as a common color space, a mechanism of transforming a viewing moving image for a movie or television (TV) from the ACES to an ideal output device color space (OCES), and a mechanism of performing color transformation from the OCES to an existing display device. As a result, it is expected to improve the efficiency of complicated image transformation and color adjustment processing in an editing process after shooting.
Matrix coefficients to be used for the IDT 1502 are determined according to sensor characteristics and spectral characteristics of a light source in a shooting scene. Conventionally, the manufacturer of an imaging apparatus incorporates matrix coefficients for input device transform based on several representative types of light sources, for example, sunlight and a halogen lamp in input device transform processing or editing software in the apparatus, thereby providing them to the user.
In the IDT 1502 as well, a light source corresponding to the light source in the shooting scene is selected from the several types of light sources incorporated in advance by the manufacturer, and applied to input device transform. On the other hand, various light sources are used as expression methods for shooting of a moving image product such as a movie or commercial. As a result, there may exist a light source which cannot be processed by only the light sources incorporated in advance by the manufacturer, the matrix coefficients of the IDT 1502 may not coincide with those of the light source in the actual shooting scene, thereby disabling accurate transformation of video data of the imaging apparatus 1501 to the ACES 1503.
In addition, the light source may change in a series of scenes. For example, there is a series of scenes in which a subject moves from inside to outside. In the IDT 1502, however, it is common practice to use a method of applying one set of matrix coefficients to one video data. Consequently, for example, even if the transformation accuracy of video data to the ACES 1503 is high in an indoor scene, the transformation accuracy may decrease in an outdoor scene.
The above problem indicates that the color of the video data changes into unexpected color by transforming the video data to the ACES 1503. In this case, in a post-process, a complicated work is required. For example, an editor who does not know the actual color of the subject has to perform color adjustment, thereby lowering the working efficiency.